Process for the production of a steering wheel for a motor vehicle

ABSTRACT

A procedure for the manufacture of a steering wheel for motor vehicles consisting of an outer covering in composite material, comprising the preparation of the covering by means of composite elements with a laminar structure, the hot forming of these elements in order to obtain a pair of complementary shells ( 13   a,    13   b ), the assembly of the shells on the opposite sides of the steering wheel, in which the body of the steering wheel consists of a metal core ( 11 ) buried inside synthetic resin, and in that at least one of the shells forming the opposite sides of the covering is equipped with a support element ( 14   a,    14   b ) which allows it to be coupled to the other shell complementary to it.

TECHNICAL FIELD

[0001] This invention refers to a procedure for the manufacture of asteering wheel for motor vehicles consisting of an external covering incomposite material.

[0002] More in particular, this invention refers to a procedure whichcomprises the preparation of composite elements with a laminarstructure, hot forming of the elements to obtain a pair of shells, eachhaving a shape corresponding to half of the steering wheel to beproduced, and assembly of the shells on the opposite sides of thesteering wheel, the body of the steering wheel consisting of a metalcore buried inside synthetic resin.

BACKGROUND ART

[0003] It is known that steering wheels for motor vehicles can consistof a structure that comprises a metal core buried inside syntheticresin, and an outer covering consisting, for example, of a bivalve shellwhich forms the part designed to be gripped and the external appearanceof the steering wheel.

[0004] One of the various procedures employed in the manufacture ofsteering wheels for motor vehicles uses two shells to form the outercovering, obtained by hot forming of suitable laminar material.

[0005] After the edges have been finished by means of mechanicalmachining, the shells are respectively applied to the opposite sides ofthe steering wheel consisting of the metal core and the synthetic resincovering.

[0006] The two shells making up the covering are then fixed to eachother on the steering wheel by means of gluing along their contact line.

[0007] The gluing of these shells often proves to be a key step in theproduction process as a whole, particularly because the thickness of theshells is minimal, generally a few tenths of a millimeter.

[0008] Some solutions are known to the background art that would tend tomake the gluing of the shells more resistant; one example is describedin the patent application EP-A1-1029770 where the edges of the shellsforming the covering are mechanically machined in such a way to obtain amale female type complementary joint that couples together when the twoshells are applied to the body of the steering wheel.

[0009] The solution proposed by the previous patent clearly tends toincrease the contact surface along the edge of the shells so as toimprove the fixing and the gluing.

[0010] The solution presented by the patent application EP-A1-1029770 isinevitably insufficient and difficult to apply when the thickness of theshells is minimal and not easy to machine; in fact the shells often tendto break and to develop cracks during the mechanical machining of theedges to form the coupling surfaces.

[0011] A further typical example in which the gluing problem becomesevident is when carbon fibre shells are used.

[0012] In the patent application EP-A1-1029771 the fixing phase of thetwo shells on the body of the steering wheel comprises a previous stagein which the support sections are applied and fixed on the syntheticresin body of the steering wheel.

[0013] These sections are shaped to form a base for the support andfixing of the two shells.

[0014] In practice the sections are normally made of metal, typicallyaluminum which permits easy clinching to the body of the steering wheeland a particular aesthetic appearance when the section is left on viewas described in the patent application EP-A1-1029771.

[0015] On the other hand, however, the use of metal material isparticularly disadvantageous in consideration of the great difference inthe coefficient of thermal expansion of these materials compared withthe materials used to manufacture the coverings.

[0016] In fact, as the steering wheels of motor vehicles are subject tohigh temperature ranges the great difference in the coefficient ofthermal expansion of these materials inevitably leads to the two shellsforming the outer covering becoming detached.

[0017] In addition to the aforesaid drawback, the procedure described inthe patent EP-A1-1029771 presents a further disadvantage inconsideration of the particular machining that the body of the steeringwheel must undergo.

[0018] The gluing or clinching of the sections must in fact be carriedout with particular precision so as to avoid problems when fitting theshells on the body of the steering wheel and the unsightly appearance ofthe end product.

[0019] Document WO-A2-0005123 describes a steering wheel comprising adecorative covering especially with decorative wood. The steering wheelframe is provided with a foam sheathing in the area (3, 4) which areprovided for the decorative covering and which comprise outer dimensionsthat are smaller than those of the remaining areas. Furthermore, theabove document describes that one dimensionally stable decorativecovering part is fastened on said foam sheathing and at least onecentering means is provided between the foam and the decorative coveringpart.

[0020] The procedure for manfacturing a steering wheel according todocument WO-A2-0005123 requires the centering of at least one of theshells on the body of the steering wheel and furthermore the gluinginvolve not only the shells but also the body of the steering wheel.These are clearly strong drawbacks since the deformations of thematerial due to the high variance of the temperatures inside the carcause an alteration in the stability of the steering wheel.

DESCRIPTION OF THE INVENTION

[0021] The present invention aims to overcome the drawbacks comprised inthe background art by means of a procedure that comprises thepreparation of composite elements with a laminar structure, hot formingof the elements to obtain a pair of shells, each having a shapecorresponding to half of the steering wheel to be produced, and assemblyof the shells on the opposite sides of the steering wheel, the body ofthe steering wheel consisting of a metal core buried inside syntheticresin.

[0022] This is achieved by means of a procedure with the featuresdescribed in the main claim.

[0023] The dependent claims describe advantageous embodiments of theinvention.

[0024] The procedure according to the present invention comprises aphase, carried out before assembly on the body of the steering wheel, inwhich the shells are fitted on internal elements designed to ensureeffective and long-lasting gluing both to the steering wheel and betweenthe two shells comprising the covering.

[0025] According to a particularly advantageous form of embodiment ofthe invention, after mechanical finishing of the relative edges anelement with the structure of a particularly thin shell, and a widercross-section than the shell to which it is applied and which will formthe outer covering of the steering wheel, is glued inside a first shellcomprising the covering and obtained by hot forming.

[0026] The second shell comprising the covering is fitted over theprojections of the inner shell applied to the first shell, being fixedby gluing.

[0027] According to a particularly advantageous form of embodiment ofthe invention, an element with the structure of a particularly thinsecond shell, and a smaller cross-section than the shell to which it isapplied, is fixed inside both shells forming the covering of thesteering wheel.

[0028] In this case, the elements are applied displaced with respect tothe edges of the shells so that one of the edges of the applied elementprojects slightly with respect to the edge of one of the shells.

[0029] Two shells are thus obtained and used to form the covering of asteering wheel for motor vehicles, having a structure at theirrespective edges which is very similar to a male female joint structureobtained without any specific machining of the edges, a process whichwould be particularly delicate in view of the minimal thickness of theshells.

[0030] This particular form of embodiment according to the inventionalso makes it possible to guarantee support and reinforcement of theshells making up the covering of the steering wheel and in the assemblystage to distribute any elastic stress on both parts of the structureand not solely on one of the two as in the previous form of embodiment.

[0031] According to another form of embodiment of the invention, theelements applied to the shells forming the covering of the steeringwheel consist of flat plates with an elongated structure.

[0032] These elements are applied to the edges of the shells to createthe coupling system as for the previously described form of embodiment.

ILLUSTRATION OF THE DRAWINGS

[0033] Other features and advantages of the invention will becomeevident on reading the following description of some forms of embodimentof the invention, given as nonbinding examples, with the help of theenclosed drawings, in which:

[0034]FIG. 1 represents, in largely schematic form, a first embodimentof a procedure for the manufacture of a steering wheel for motorvehicles according to the present invention;

[0035]FIG. 2 represents, in largely schematic form, a second embodimentof a procedure for the manufacture of a steering wheel for motorvehicles according to the present invention;

[0036]FIG. 3 represents, in largely schematic form, a third embodimentof a procedure for the manufacture of a steering wheel for motorvehicles according to the present invention;

[0037]FIGS. 4 and 5 represent two respective cross sections of asteering wheel for motor vehicles manufactured by means of two forms ofembodiment of the procedure according to the present invention.

DESCRIPTION OF SOME FORMS OF EMBODIMENT

[0038] A classic steering wheel for motor vehicles normally comprises acentral part or hub, a plurality of radial spokes and an outer edge.

[0039] As is known from forms of embodiment comprised in the backgroundart, the outer edge 10 consists of a metal core 11 buried insidesynthetic resin 12.

[0040] This is all enclosed in an outer casing consisting for example ofa covering 13.

[0041] This covering 13 generally consists of two shells 13 a, 13 bsuperimposed one on the other and joined together.

[0042] These shells 13 a, 13 b may be produced for example by means ofthe forming of glass fibre or carbon fibre materials with a laminarstructure according to known procedures and additionally treated andmachined in order to provide the structure with features of rigidity andgripping stability.

[0043] The shells obtained by means of these machining processes, asshown in FIGS. 1 to 3, comprise a convex external side, a concaveinternal side and edges.

[0044] According to a first form of embodiment of the present invention,shown in FIG. 1, elements 14 a, 14 b which may be made from compositematerial are applied to the inner side of the shells 13 a, 13 b andconstitute the system which connects and fixes the two shells 13 a, 13 bforming the covering 13.

[0045] According to a second form of embodiment of the presentinvention, shown in FIGS. 2 and 4, a similar element 14 is applied tothe inner side of the shell 13 a in such a way that the edges of thiselement 14 project with respect to the edges of the shell 13 a and cancouple and be joined for example by means of gluing to the edges of thesecond shell 13 b forming the covering of the steering wheel

[0046] According to a third form of embodiment of the present invention,shown in FIGS. 3 and 5, an element 14 a, 14 b is applied to the innerside of both shells 13 a and 13 b near a respective edge in such a waythat the edges of this element 14 project with respect to the edges ofthe shell 13 a and can couple and be joined for example by means ofgluing to the edges of the second shell 13 b forming the covering of thesteering wheel.

[0047] The elements 14 a and 14 b applied to the shells 13 a and 13 bforming the covering of the steering wheel consist in this case of flatplates to be applied, for example by means of gluing, to the edges ofthe inner sides of the shells.

[0048] In detail, the plates 14 a and 14 b can be glued either to justone of the shells or to both of them, and either to one edge of theshell or to both edges.

[0049] The edge of each plate 14 a, 14 b projects from the edge of oneof the shells in such a way that it can couple with the edge of theother shell forming the covering and be glued to it.

[0050] The invention was previously described with reference to somepreferred forms of embodiment of the same.

[0051] However it is clear that the present is susceptible to severalvariations within the scope of the present invention, in the field ofthe technical equivalences.

1. A process for the production of a steering wheel for motor vehicles,comprising the steps of: providing a substantially circular-shaped metalcore (11); burying said metal core (11) inside a synthetic resin (12),thereby forming a steering wheel body; preparing a pair of outercovering shells (13 a, 13 b) by means of hot forming of compositeelements with a laminated structure, said shells (13 a, 13 b) having acomplementary shape and being suitable to be placed over said steeringwheel body and joined together along their edges; preparing a system(14) for connecting and fastening to each other said shells (13 a,13.b), said system being constituted by a thin element (14) that isfixed to the inner side of one (13 a) of said shells in such a way thatboth edges of said thin element (14) protrude over the edges of saidshell (13 a), whereby the surface of said thin element (14) protrudingover the edges of said shell (13 a) forms an area for fastening saidthin element (14) to the inner side of the other shell (13 b); andjoining said two shells (13 a, 13 b) together along their edges, therebyfixing said other shell (13 b) to the said protruding surface of saidthin element (14).
 2. A process for the production of a steering wheelfor motor vehicles, comprising the steps of: providing a substantiallycircular-shaped metal core (11); burying said metal core (11) inside asynthetic resin (12), thereby forming a steering wheel body; preparing apair of outer covering shells (13 a, 13 b) by means of hot forming ofcomposite elements with a laminated structure, said shells (13 a, 13 b)having a complementary shape and being suitable to be placed over saidsteering wheel body and joined together along their edges; preparing asystem (14 a, 14 b) for connecting and fastening to each other saidshells (13 a, 13 b), said system being constituted by a pair of thinelements (14 a, 14 b), each thin element (14 a, 14 b) being fixed to theinner side of a respective shell (13 a, 13 b) in such a way that an edgeof said thin element (14 a, 14 b) protrudes over an edge of saidrespective shell (13 a, 13 b), whereby the surface of said thin element(14 a, 14 b) protruding over the edge of said respective shell (13 a, 13b) f:o˜rms an area for fastening said thin element (14 a, 14 b) to theinner side of the other respective shell (13 a, 13 b); and joining saidtwo shells (13 a, 13 b) together along their edges, thereby fixing eachrespective shell (13 a, 13 b) to the said protruding surface of saidthin elements (14 a, 14 b).
 3. A process according to claim 1, whereinsaid shells (13 a, 13 b) are joined together by glueing.
 4. A steeringwheel for motor vehicles characterized in that it is manufactured by aprocess according to claim
 1. 5. A steering wheel for motor vehiclescomprising a substantially circular-shaped metal core (11) buried insidea synthetic resin (12), thereby forming a steering wheel body, as wellas a pair of outer covering shells (13 a, 13 b) formed by compositeelements with a laminated structure, said shells (13 a, 13 b) having acomplementary shape and being placed over said steering wheel body andjoined together along their edges; characterised in that it furthercomprises a system (14) for connecting and fastening to each other saidshells (13 a, 13 b), said system being constituted by a thin element(14) that is fixed to the inner side of one (13 a) of said shells insuch a way that both edges of said thin element (14) protrude over theedges of said shell (13 a), whereby the surface of said thin element(14) protruding over the edges of said shell (13 a) forms an area wheresaid thin element (14) is fastened to the inner side of the other shell(13 b).
 6. A steering wheel for motor vehicles comprising asubstantially circular-shaped metal core (13) buried inside a syntheticresin (12), thereby forming a steering wheel body, as well as a pair ofouter covering shells (13 a, 13 b˜formed by composite elements with alaminated structure, said shells (13 a, 13 b) having a complementaryshape and˜being placed over said steering wheel body and ˜oined togetheralong their edges; cha.racterised in that it further comprises a system(ida, ib) for connecting and fastening to each other said shells (1-3 a,13 b), said system being constituted by a pair of thin elements (14 a,14 b), each thin element (14 a, 14 b) being fixed to the inner side of arespective shell (13 a, 13 b) in such a way that an edge of said thinelement (14 a, 14 b) protrudes over an edge of said respective shell (13a, 13 b), whereby the surface of said thin element (114 a, 14 b)protruding over the edge of said respective shell˜(13 a, 13 b) forms anarea where said thin element (].4 a, 14 b) is fastened to the inner sideof the other respective shell (13 a, 13 b).
 7. A process according toclaim 2, wherein said shells (13 a, 13 b) are joined together byglueing.
 8. A steering wheel for motor vehicles characterized in that itis manufactured by a process according to claim 1.